For wireless communication at data rates above about 1 Gbit/s, a frequency band of about 7 GHz has been allocated around about 60 GHz. In this frequency band several applications are targeted with mass-market potential. For example wireless High Definition Multi-media Interface (HDMI), wireless Universal Serial Bus (USB) or SYNC-and-GO, allowing fast data download, are very interesting application for the consumer market. For wireless consumer products, the key elements are low price and low power consumption. Considering possible implementation technology, CMOS is preferred as it allows for integration of both digital and analog blocks on a single chip. Moreover, downscaled digital CMOS—a cheap technology for large-volume products—is capable of handling radio frequency signals with a carrier frequency of about 60 GHz and with baseband bandwidths up to about 1 GHz. To relax the link budget (i.e. the gain and the output power of the transmitter), often beam-forming, which requires multiple antenna paths at the receiver and the transmitter sides, is used. Compact designs occupying small chip area and consuming low power are essential for beam-forming transceivers operating at about 60 GHz.
For a radio receiver operating at millimeter-waves the most challenging tasks are the design and implementation of the blocks operating directly at the radio frequency, i.e. so called radio frequency (RF) building blocks. A simplified block scheme of a wireless receiver operating at millimeter-waves is shown in FIG. 1. The LNA and the down-conversion mixers (MIX) form the RF front-end, and they amplify and down-convert the received RF signal to low (baseband) frequencies. The signal is further processed by the baseband (BB) blocks.
The design challenge comes from the fact that the RF front-end (i.e. the LNA and MIX blocks) are tuned circuits, which intensively use inductive passive elements (inductors or transformers) to tune out/cancel parasitic capacitances. As a consequence different resonant circuits are created in the front-end. Accurate prediction of the resonant frequencies and mutual dependence of these resonant circuits have direct influence on performance of RF building blocks. In addition, since the RF building blocks operate directly at mm-wave frequencies, they represent the most power hungry part of a radio receiver as well as the strongest noise contributor.
Different radio receiver architectures operating at millimeter-waves have been proposed. However, they primarily focus on proposing optimal designs for only one of the RF front-end blocks, e.g. the LNA block. For example, Borremans et al. (“A digitally controlled compact 57-to-66 GHz front-end in 45 nm digital CMOS”, IEEE ISSCC 2009, pp. 492-493, 493a, February 2009) propose a 60 GHz low noise direct-downconversion front-end with a two-stage cascode LNA and a conventional current-commutating down-conversion mixer (so called Gilbert-type mixer). Khanpour et al. propose in “A Wideband W-Band Receiver Front-End in 65-nm CMOS” (IEEE ISSCC 2008, vol. 43, no. 8, pp. 1717-1730, August 2008) a wideband front-end with a three-stage cascode LNA with transformer feedback and double-balanced Gilbert-cell mixers. Weyers et al. (“A 22.3 dB Voltage Gain 6.1 dB NF 60 GHz LNA in 65 nm CMOS with Differential Output”, IEEE ISSCC 2008, pp. 192-606, February 2008) propose a LNA with two inductively-coupled cascode amplifiers and an output buffer, which can be directly connected to double-balanced Gilbert-cell mixers. However, there are a couple of problems associated with the proposed solutions. First, the layout is bulky because they use several inductors per stage. This increases the sensitivity to parasitics and modeling inaccuracies. Second, the ESD protection, which is made by using diodes, introduces penalty to the noise figure. It is difficult to achieve noise figure lower than 7 dB using proposed solutions. Further, these conventional architectures suffer from high current losses as they use current-commutating mixer.
Document WO01/52431 presents a receiver RF front-end with two-step down-conversion. The application is mainly concerned with the issues typical for two-step down-conversion front-ends. For example, it explains how the image can be rejected by the LNA before first down-conversion.
In WO2009/035665, a low-noise amplifier suitable for operation at low-frequencies is presented. It is fully based on feedback and it cannot be at all used at 60 GHz. The presented feedback configurations simply cannot be used at 60 GHz because the active element (amplifier) cannot provide sufficient gain.
Application WO2007/068547 deals with a frequency division multiplex system for wireless communications. In this system the receiver and the transmitter are both on and the strong transmit signal is a strong interferer for the weak received signal. One mainly focuses on the way the receiver can suppress the strong signal coming from the transmitter.
It becomes apparent that there is a need for providing a low power, cost and area efficient front-end solution for wireless devices operating at mm-waves.